JPH0718186Y2 - Signal processor - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is directed to, for example, FM compression of an audio signal along with time axis compression.
The present invention relates to a signal processing apparatus suitable for being applied to a magnetic recording / reproducing apparatus capable of performing modulation and recording on an inclined recording track of a magnetic tape using a rotating magnetic head and reproducing the same.

2. Description of the Related Art Conventionally, as a rotary magnetic head type video tape recorder capable of recording and reproducing, various ones using a small drum have been proposed for downsizing of the apparatus.

FIG. 3 shows an example of the recording system of such a video tape recorder. In the figure, 1 is an input terminal to which a video signal SV is supplied, and the video signal SV supplied to this input terminal 1 is supplied to a memory 3 via an A / D converter 2 and sequentially written, The video signal SV read from the memory 3 is supplied to a low-pass filter 5 for extracting a luminance signal and a band-pass filter 6 for extracting a carrier color signal via a D / A converter 4.

In this case, the read frequency of the memory 3 is 1.2 times the write frequency, and is written in the memory 3 every 1/60 seconds.
The video signal SV for the field is 1/60 × 1/1 from the memory 3.
It is read in 2 seconds and compressed on the time axis. At this time, the color subcarrier frequency changes from 3.58 MHz to 4.29 MHz.

The luminance signal Y obtained from the low-pass filter 5 is FM.
It is supplied to the modulator 7 and modulated. In this case, the sync chip is 5.04 MHz, the white peak is 6.48 MHz, and the frequency deviation is modulated to be 1.44 MHz. This FM modulator 7
The FM luminance signal YFM output from the output is supplied to the adder 8.

Further, the carrier color signal C obtained by the bandpass filter 6
Is supplied to the frequency converter 9 for frequency conversion. In this case, the color subcarrier frequency is converted from 4.29 MHz to 892 KHz to a low frequency. The low frequency conversion color signal CL output from the frequency converter 9 is supplied to the adder 8.

Further, 11 is an input terminal to which the audio signal SA is supplied, and the audio signal SA supplied to this input terminal 11 is supplied to the memory 13 via the A / D converter 12 and sequentially written,
The audio signal SA read from this memory 13 is the D / A converter 1
It is supplied to the FM modulator 15 via 4. In this case, memory 1
The read frequency of 3 is 1.2 times the write frequency and is written in the memory 13 every 1/60 seconds. The audio signal SA (corresponding to one field of the video signal SV) is
It is read out at 60 × 1 / 1.2 seconds and compressed on the time axis.

Further, the audio signal SA supplied to the FM modulator 15 is FM-modulated so that the carrier frequency becomes 1.8 MHz. This FM modulator 15
The FM audio signal AFM output by the above is supplied to the adder 8.

The adder 8 outputs a frequency multiplex signal of the FM luminance signal YFM, the low frequency conversion color signal CL and the FM audio signal AFM. Fourth
FIG. B shows the frequency spectrum of this frequency-multiplexed signal. Then, this frequency-multiplexed signal is obtained by compressing the video signal SV and the audio signal SA on the time axis as described above, and in each field period (1/60 seconds), for example, 1/60 × 1 / It will exist for 1.2 seconds. This frequency-multiplexed signal is transferred via the recording amplifier 21 to the selector switch 22.
Is supplied to. The changeover switch 22 is alternately switched to the a side and the b side every one field period. The frequency-multiplexed signals obtained at the fixed terminals on the a side and the b side of the changeover switch 22 are supplied to the rotary magnetic heads HA and HB, respectively.

These magnetic heads HA and HB, as shown in FIG.
Installed in close proximity, for example with an angular spacing of 1.5H,
It is rotated in the direction of arrow DH at the field frequency (60Hz). The magnetic heads HA and HB are different from each other in the angle of the differential gap, so-called azimuth angle. Also, 23 is a magnetic tape, and 30 is attached to the peripheral surface of the drum 24.
It is wound diagonally over an angular range of slightly over 0 ° and driven at a predetermined speed in the direction of arrow DT.

As described above, the frequency-multiplexed signal supplied to the magnetic heads HA and HB is the one that existed in 1/60 × 1 / 1.2 seconds from the beginning of each field period (1/60 seconds), and the magnetic head HA , And HB can be rotated by 300 ° in 1/60 × 1 / 1.2 seconds, so that the magnetic head HA and HB can record a length of 300 ° on the magnetic tape 23, as shown in FIG. The tracks TA and TB are alternately formed to record a signal.

In order to reproduce what is recorded on the magnetic tape 23 in this way, the magnetic head HA of the rotary head device shown in FIG.
And the signal reproduced by HB is subjected to signal processing by processing reverse to the recording signal processing of FIG.

The recording format of FIG. 6 is based on two rotating magnetic heads, each of which has a magnetic tape wound around a drum in a range of 180 °, is attached at an angular interval of 180 °, and is rotated at a frame frequency (30 Hz). , Frequency-multiplexed signals without time axis compression as shown in FIG.
It is the same as that recorded on the recording tracks TA and TB having a length of 0 °. Therefore, it is of course possible to reproduce the same even by a video tape recorder having a large drum rotary head device in which two rotary magnetic heads are mounted at an angular interval of 180 ° from each other, and it is compatible.

In this case, of course, the time axis expansion processing is unnecessary in the reproduction signal processing.

By the way, in the recording system of the video tape recorder of FIG. 3, in order to remove the noise mixed in by the D / A converter 14, the third system is provided between the D / A converter 14 and the FM modulator 15. A filter 16 is inserted as shown by a broken line in the figure.

[Problems to be Solved by the Invention] The signal supplied to the filter 16 is the audio signal SA which is time-axis compressed as described above, and as shown in FIG. 7A, each field period (1/60 1/60 × 1 / from the beginning
The audio signal SA exists in the period ta of 1.2 seconds, but the other period tb is a non-signal period in which the audio signal SA does not exist and only the DC component exists. Therefore, the output signal of the filter 16 is one in which the DC component in the no signal period is lost as shown in FIG.

When the DC component is lost in the filter 16 as described above, there is a disadvantage that the FM modulator 15 does not perform the correct FM modulation such that the level change of the signal becomes large and the FM modulator 15 overmodulates.

The present invention takes these points into consideration, and aims to restore the DC component lost by the filter so that FM modulation can be performed correctly, for example.

[Technical Means for Solving Problems] In order to solve the above problems, in the present invention, a first signal that has passed a filter and has lost a DC component and a second signal that does not pass the filter. And a low-pass filter for extracting a DC component from the output signal of the comparing means, and an adding means for adding the output signal of the low-pass filter and the first signal. .

[Operation] In the configuration described above, the DC component lost in the filter 16 is extracted from the low-pass filters 41 and 42. And
This DC component passes through the filter 16 and is added to the signal that has lost the DC component in the adder 36, so that the signal in which the DC component is restored is output from this adder 36.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, the output signal of the filter 16 is supplied to the DC component correction circuit 17. Further, the output signal of the D / A converter 14 is supplied to the DC component correction circuit 17. Then, in this DC component correction circuit 17, the DC component is restored by superimposing the DC component on the signal which has passed through the filter 16 and has lost the DC component.

The signal whose DC component has been restored by this DC component correction circuit 17
It is supplied to the FM modulator 15.

FIG. 2 shows a specific configuration example of the DC component correction circuit 17.

In the figure, 31 is an input terminal to which a signal (shown in FIG. 7B) in which the DC component has been lost is supplied through the filter 16. The signal supplied to the input terminal 31 is supplied to the non-inverting input terminal of the operational amplifier 32 for gain adjustment and impedance conversion. The output side of this operational amplifier 32 is a resistor
Grounded through a series circuit of 33 and 34
The connection point of 34 and 34 is connected to the inverting input terminal of the operational amplifier 32. The output signal of the operational amplifier 32 is the resistor 35.
Op-amp 36 for addition and impedance conversion via
Is supplied to the non-inverting input terminal of.

Further, the output signal of the operational amplifier 32 is supplied to the inverting input terminal of the operational amplifier 38 which constitutes the comparator via the resistor 37,
The output side of the operational amplifier 38 is connected to the inverting input terminal of the operational amplifier 38 via the resistor 39. Reference numeral 40 is an input terminal to which the output signal of the D / A converter 14, that is, the signal which does not pass through the filter 16 (shown in FIG. 7A) is supplied. The signal supplied to the input terminal 40 is supplied to the non-inverting input terminal of the operational amplifier 38.

Therefore, the output side of this operational amplifier 38 has a filter 16
A DC component and an AC component lost at are obtained.

The output side of the operational amplifier 38 is grounded via a series circuit of a resistor 41 and a capacitor 42 which form a low pass filter. The output side of this low-pass filter, namely resistor 41
Only the DC component lost in the filter 16 (shown in FIG. 7C) is obtained at the connection point of the capacitor 42 and the capacitor 42, and this DC component is supplied to the non-inverting input terminal of the operational amplifier 36 via the resistor 43. .

Therefore, in this operational amplifier 36,
The DC component output from the low-pass filter is added to the signal in which the DC component is lost after passing through the filter 16 output from 32, and the signal in which the DC component is restored is obtained. Be derived to.

As described above, according to this example, in the DC component correction circuit 17, the DC component lost by passing through the filter 16 is restored,
The signal in which the DC component is restored is supplied to the FM modulator 15, so that the FM modulator 15 can perform good FM modulation without any inconvenience such as overmodulation.

In the above embodiment, the present invention is applied to the recording system of a video tape recorder capable of recording and reproducing, but the present invention needs to restore the DC component lost by passing through the filter. It can be similarly applied to other cases.

[Advantages of the Invention] According to the present invention described above, the DC component lost by passing through the filter is restored.
Even if a noise removal filter is placed after the A converter, there is no inconvenience such as overmodulation, and the FM
Modulation can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a specific configuration of a DC component correction circuit, FIG. 3 is a diagram showing an example of a recording system of a video tape recorder, and FIG. ~ Fig. 6 is a diagram for explaining it, and Fig. 7 is a diagram for explaining the operation of the embodiment. 15 …… FM modulator 16 …… Noise removal filter 17 …… DC component correction circuit

Claims (1)

[Scope of utility model registration request] 1. A first DC component which has passed a filter and has lost a DC component.
Means for comparing the second signal that does not pass through the filter, a low-pass filter for extracting a DC component from the output signal of the comparing means, and an output signal of the low-pass filter and the first signal And a signal processing device that includes an adding unit that performs.